The present invention relates to an electric screen device for preventing creatures, such as fishes and shellfishes, from intruding into a water intake port, i.e., a water intake channel or the like in a power plant or the like.
To prevent creatures, such as fishes and shellfishes, from intruding into a water intake port in a power plant, a water intake channel is provided with an electric screen device.
Conventionally, this electric screen device comprises a pair of opposed electrode assemblies disposed on opposite side walls of the water intake channel, and a voltage applying device for applying dc or ac voltage between said electrode assemblies at predetermined intervals of time.
Thus, an electric screen is formed by a predetermined voltage applied between said electrode assemblies at predetermined intervals of time by the voltage applying device.
The applied voltage is of a value such that the product of the peak value of the intensity of an electric field and the voltage applying time (on-time) is not less than 0.01 V sec/cm, and the off-time is set within the range of 0.5-3 sec. Empirically, it has been so set for the case of sweetfish of 10 cm length that the peak value of the electric field intensity is 0.08 V/cm and the on-time and off-time are respectively 2 sec.
According to the electric screen device described above, however, the off-time is relatively long, which fact is preferable from the viewpoint of power saving but poses a problem that it permits intrusion of creatures.
Accordingly, it is an object of the invention to provide an electric screen device which is designed to save power and to reliably prevent intrusion of creatures.
An electric screen device according to the present invention comprises a pair of opposed electrode assemblies disposed on opposite sides of a water channel, and a dc pulse applying device for applying dc pulse voltage between said electrode assemblies to prevent creatures from intruding into the water channel, said electric screen device being characterized in that the product of the peak value of the field intensity (voltage per unit of length) of an electric field produced between said electrode assemblies by said dc pulse applying device and the body length (unit of length) of creatures to be prevented from intrusion into the water channel is not less than 0.1 V and in that the dc pulse applying time is within 2-200 msec. Further, in the above arrangement, the duty factor of the dc pulses is not more than 0.5.
According to the above arrangement, since the product of the peak value of the intensity of the electric field produced between the electrode assemblies disposed on opposite sides of the water channel and the body length of creatures to be prevented from intrusion is not less than 0.1 V, and since the dc pulse applying time is within the range of 2-200 msec, intrusion of the creatures can be efficiently prevented.